1. Field of the Invention
This invention is related to nonvolatile semiconductor memory device which can reprogram data in bits or byte units.
2. Description of the Prior Art
Recently, LSI such as a microcomputer are being incorporated into a variety of devices, and demands for storing small to medium amounts of data in a nonvolatile way to each of these many LSI are also increasing. In order to achieve such aims, a medium amount of memory is sufficient as a nonvolatile memory. However, data which is reprogrammable in smaller units (1 byte to a few bytes) is being demanded.
However, flash memory represented by a NAND type has large capacity and low cost and is presently widely being used. However, in flash memory, programming is performed in byte to page units (about 1 kb), erasure is performed in page units (about 1 kb) to blocks (about 64 kb) and therefore does not satisfy the reprogramming unit requested for the programming purposes stated above.
Conventionally, memory such as pFLASH (registered trademark) (refer to Patent Document 1) and NeoFlash (registered trademark) (refer to Patent Document 2) have been proposed.
Background arts to this invention are described, in more detail, in WO99/19880; U.S. Pat. No. 7,250,654; Japanese Patent Publications 2006-156925, 2006-128594, and 2006-269697; and U.S. Pat. No. 5,687,118, incorporated herein as a reference.